It is known in the art that various fuse technologies, such as electrically activated or laser activated fuses have been advantageously used over the years in a variety of products. Attempts have been made in the past to interconnect fuses of different fuse technologies in the same circuitry to benefit from the advantages offered by the different types of fusing technologies. By way of example, in U.S. Pat. No. 5,748,031 issued to Best, a laser fuse and an electrical fuse are interconnected in series in the same circuit such that fusing is accomplished by either using a laser to blow one fuse or passing a current and programming the fuses in series with it. In another example, in U.S. Pat. Nos. 5,485,032 and 5,314,840 to Schepis et al., of common assignee, a fuse is described which can be optically programmed by laser or blown by an electrical current and which exhibits a change in resistance when compared to an unprogrammed fuse, wherein the change in resistance is induced by alloying aluminum and germanium. In yet another example, in U.S. Pat. Nos. 5,340,775 and 5,285,099 to Carruthers et al., and of common assignee, a SiCr fuse is described having the dual purpose of serving as a fuse which can be optically or electrically programmed. In still another example, in Japanese Patent 6-325589 issued in 1994, a circuit is described which contains laser and electrical fuses wherein laser fuses are used to control the electrical fuses to reduce total circuit area. Here again a laser and an electrical fuse are electrically coupled to each other, allowing one to control the other.
Linking laser activated fuses to electrically activated fuses in the same circuit has a distinct disadvantage in that having the same number of laser fuses and electrical fuses in each circuit imposes a severe penalty in the amount of chip real estate that is consumed. Alternatively, if only some laser fuses were coupled on the same circuit to electrical type fuses, much of the flexibility in activating redundancies would be lost since only those laser fuses that are unattached at the wafer level could be used in order not to render any electrical fuse unusable later on at the module level.
Laser activated fuses are known to be much reliable than electrical fuses. Yet, several drawbacks, fully described in, e.g., the aforementioned U.S. Pat. No. 5,748,031, makes them less desirable than electrical fuses. By way of example, laser programmable fuses have a distinct disadvantage of requiring optical contact to blow the fuse. More specifically, the laser programmable fuse must be placed on the chip with its link fuse exposed by a window to allow the beam to break the link whenever programming is desired. However, once the chip is placed in a module or in some other second level package, the window is no longer accessible and the laser fuse can no longer be programmed at will. Thus, laser activated fuses are useful only to chips, namely, to pre-packaged integrated circuit (IC) devices but not to chips mounted on a module.
Electrically programmable fuses have the advantage of being easily programmed no matter where the fuses are located, whether on a chip, module, and the like, with the window exposed or whether placed deep inside the semiconductor structure. Electrical fuses use bonding pads to interface with fuse zapping tools. These pads can be placed outside the package, which provides the added flexibility of blowing the fuse regardless whether or not the IC chip is mounted on the next level of packaging. Yet, they have the distinct disadvantage of occupying a substantial amount of chip real estate, a serious drawback, particularly in high density integrated circuit chips.